An ophthalmic apparatus is equipped with an alignment device which performs an alignment between an eye to be examined and a measurement optical system or an observation optical system in the ophthalmic apparatus.
Conventionally, in the alignment between the ophthalmic apparatus and the eye to be examined, an alignment light is projected to the eve to be examined, the reflection light from the eye to be examined is received by a photodetection element and the alignment is executed based on a photodetecting position of the reflection light.
For example, in the alignment (an X alignment or a Y alignment) in a direction (an X direction or a Y direction) orthogonal with respect to a measurement optical axis of the measurement optical system, the alignment light is projected to the eye to be examined from the measurement optical axis, the reflection light is received by the photodetection element, a deviation between the measurement optical axis and a photodetecting position is obtained on the photodetection element, and the measurement optical system is moved in the X direction and the Y direction so that the deviation is eliminated.
Further, in the alignment (a Z alignment) in a Z direction, the alignment light is entered with respect to the measurement optical axis at a predetermined angle and the reflection light is received, by the photodetection element. When the eye to be examined moves in a measurement optical axis direction, since the photodetecting position on the photodetection element changes according to a principle of optical lever, the measurement optical system is moved in the Z direction so that a deviation between an actual photodetecting position and a photodetecting position when aligned is eliminated.
It is to be noted that, since an accuracy of approximately 30 μm is required in the alignment in the Z direction, a coarse alignment optical system and a precise alignment system which has a higher magnification than the coarse alignment optical system are usually provided, the alignment is first performed in a predetermined range by the coarse alignment optical system, and a precise alignment is performed next by the precise alignment optical system.
The coarse alignment optical system and the precise alignment optical system are independent optical systems, photodetection elements for the coarse alignment and the precise alignment are provided respectively, an alignment light for the coarse alignment is emitted, the reflection light from the eye to be examined is received by the photodetection element for coarse alignment and the coarse alignment is executed, the processing is switched over to the alignment by the precise alignment optical system when fallen within a predetermined alignment range and the precise alignment is executed.
In a conventional alignment device, in a case of performing the alignment in the Z direction in particular, the coarse alignment and the precise alignment are performed respectively based on the signals from the different photodetection elements, i.e., the photodetection element for coarse alignment and the photodetection element for precise alignment. For this reason, it is necessary to perform a signal processing and a processing control for each of the photodetection element for coarse alignment and the photodetection element for precise alignment respectively, and hence a signal processing circuit becomes complicated. Further, since the signals from the different photodetection elements are switched over and then used, a simultaneousness of the signals become a problem. That is, a discontinuation of the signals occur while the signals are switched over, and a delay on a circuit occurs in association with the switching over of the signals.
For this reason, in a case where there is a change such as a movement of the eye to be examined, etc. in the switching over of the signals, for example, when blinking is performed and the like, a signal from the photodetection element or course alignment is greatly different from a signal from the photodetection element for precise alignment, and the coarse alignment cannot be shifted to the precise alignment. In such a case, the processing returns to the coarse alignment, the coarse alignment is performed again, and further, a process to shift to the precise alignment is carried out.
For this reason, conventionally, there was a problem that there is a case where the coarse alignment cannot be smoothly shifted to the precise alignment.